Layered compounds of mixed oxides and Lewis bases

ABSTRACT

A new composition of matter comprising the reaction product of a mixed oxide having layers of corner linked octahedra and tetrahedra and a Lewis base. The reaction product forms a layered compound of the formula L x  MOM&#39;O 4  where MOM&#39;O 4  is a mixed oxide selected from the group consisting of VOPO 4 , VOSO 4 , VOAsO 4 , VOMoO 4 , NbOPO 4 , NbOAsO 4 , TaOPO 4  and MoOPO 4 , x is from about 0.1 to 1.0 and L is a Lewis base containing nitrogen or oxygen electron donor and is selected from the group consisting of 5-membered heterocyclic amines, 6-membered heterocyclic amines, amine oxides, triorganophosphates, phosphine oxides and sulfoxides. The layered compounds are characterized in that L is covalently bound to a metal atom in the MOM&#39;O 4  layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.205,141 filed Nov. 10, 1980, now U.S. Pat. No. 4,355,162.

BACKGROUND OF THE INVENTION

This invention relates to unique layered compounds formed by reactingmixed oxides with a Lewis base. More particularly, the Lewis base iscovalently bound to a metal atom within a layered oxide structure.

It is known from U.S. Pat. No. 3,766,064 that heavy metal chalcogenideswherein the metal is titanium, vanadium, zirconium, niobium, hafnium,tantalum, palladium, platinum and gallium, and the chalcogenide issulfur, selenium and tellurium can be intercalculated with ammonia,hydrazine and organic nitrogen compounds. The general properties andmethods of preparation are described therein. U.S. Pat. No. 3,688,109relates to similar intercalated compounds useful as X-ray diffractiongrating crystals. Intercalation compounds including molybdenum andtungsten with isonitrile and metallocene guests are disclosed in U.S.Pat. Nos. 4,094,893 and 3,980,684. U.S. Pat. No. 4,049,887 relates to animproved cathode containing as active material a layered compound of theformula MA_(x) B_(y) where M is Fe, V, Ti, Cr or In, A is O, S, Se or Teand B is Cl, Br or I.

J. Bernard and M. Camelot, C. R. Acad. Sci., Paris, Ser. C., 263:1068(1966) report on the reaction of molybdenum trioxide, molybdenylchloride and the molybdenum dioxydichloride with pyridine. In asubsequent work, M. Camelot, Revue de Chimie Minerale, 6, 853 (1969),studied addition compounds of pyridine with some oxychlorides ortrioxides of chromium, molybdenum and uranium. Based on an infraredspectroscopic investigation, Camelot concluded that these compounds weremolecular coordination compounds.

G. Lawdig (Z. Anorg. Allg. Chem., 338, 266 (1965)) relates to astructural study of VPO₅.nH₂ O. It is reported on pages 273 and 274 thatanhydrous VPO₅ takes up ammonia and amines with a one-dimensionallattice expansion to give a VPO₅.1.1NH₃ reaction product. Pyridine wasstated to show no lattice expansion. Hydrogen bonding was asserted to beimportant in determining the type of molecule that can react with VPO₅layers. Similar structural studies involving niobium phosphate arereported by Chernorukov et al., Russian J. Inorg. Chem., 23, 1627(1978); 24, 987 (1979).

SUMMARY OF THE INVENTION

It has been discovered that certain mixed oxides form new compoundshaving a unique layered structure. The composition of the inventioncomprises the reaction product of a mixed oxide having layers of cornerlinked octahedra and tetrahedra and a Lewis base, said reaction productforming a layered compound of the formula L_(x) MOM'O₄ where MOM'O₄ is amixed oxide selected from the group consisting of VOPO₄, VOSO₄, VOAsO₄,VOMoO₄, NbOPO₄, NbOAsO₄, TaOPO₄ and MoOPO₄, x is from about 0.1 to 1 andL is a Lewis base containing nitrogen or oxygen electron donors andselected from the group consisting of 5-membered heterocyclic amines,6-membered heterocyclic amines, amine oxides, triorganophosphates,phosphine oxides and sulfoxides, the layered compound beingcharacterized in that L is covalently bound to a metal atom in theMOM'O₄ layer. When prepared in the presence of a proton source, thelayered structure is partially protonated to form a compound of theformula L_(x) H_(y) MOM'O₄, L, x and MOM'O₄ being defined above, H ishydrogen and y ranges from about 0.1 to about 0.5.

The present compositions contain a neutral Lewis base which iscovalently bound to a metal (M) atom in the mixed oxide (MOM'O₄) layers.The bonding is therefore similar to that which might be expected from atypical coordination complex. They are not, however, coordinationcomplexes because of the layered structure which remains even afterreaction with Lewis base.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a schematic diagram of the bonding arrangement in(pyridine)VOPO₄.

DETAILED DESCRIPTION OF THE INVENTION

Lewis bases which form the layered compounds of the formula L_(x) MOM'O₄are those which have heterocyclic nitrogen and oxygen donors, preferably5- and 6-membered heterocyclic nitrogen donors, and x is preferably fromabout 0.4 to 1.0. Preferred nitrogen donors are pyridines having theformula ##STR1## where R is hydrogen, halogen; C₁ -C₂₀, preferably C₁-C₁₀ aliphatic; C₆ -C₁₀ aryl, preferably phenyl which may be substitutedby halogen or C₁ -C₆ alkyl; C₇ -C₂₀ aralkyl, preferably benzyl orphenylethyl; OR' or SR' where R' is C₁ -C₆ alkyl. Examples are ##STR2##Other 5- and 6-membered heterocyclic amines which may form layeredcompounds include pyridazine, pyrimidine, pyrazine, triazine,N-substituted oxazine, N-substituted imidazole, oxazole, thiazole,1,4-diazabicyclo[2,2,2]octane and ##STR3## where n is 0 or 1 and R² ismethylene; alkylene; alkenylene or alkynylene of 2-6 carbon atoms; C₆-C₁₀ aryl, preferably paraphenylene, C₇ -C₁₄ aralkylene; oxygen orsulfur. Oxygen donors may be amine oxides, triorganophosphates,phosphine oxides and sulfoxides.

Mixed oxides according to the invention are characterized in terms oflayers of corner linked octahedra and tetrahedra, the layers beinglinked through the apical octahedron oxygens. The octahedra, however,are severely distorted with one very short and one very longmetal-oxygen bond so that the resulting structure is actually layeredrather than a three dimensional net. Mixed oxides may be hydrated, withthe long metal-oxygen bond replaced by a coordinated water molecule. Thelayers in this instance are held together by hydrogen bonding. In theformula MOM'O₄, M is V, Nb, Ta or Mo and M' is P, As, S or Mo. Examplesof mixed oxides which have the above-cited structural features areVOPO₄, VOSO₄ VOAsO₄, VOMoO₄, NbOPO₄, NbOAsO₄, TaOPO₄ and MoOPO₄.Preferred mixed oxides are VOSO₄, VOPO₄, VOAsO₄ and VOMoO₄, especiallyVOAsO₄ and VOPO₄.

If L_(x) MOM'O₄ is prepared in the presence of a proton source such asH₂ O or Bronsted acid, the layered structure is at least partiallyprotonated to form a compound of the formula L_(x) H_(y) MOM'O₄ where L,x, MOM'O₄ are defined as hereinbefore, H is hydrogen and y is from about0.1 to about 0.5. While the precise structure is not known, protonationresults in a change in the IR spectrum at about 1600 cm⁻¹, an enhancedesr signal and increased thermal stability.

The present mixed oxides of the formula MOM'O₄ are described in theliterature, e.g., A. F. Wells, Structural Inorganic Chemistry, 4th ed.,Oxford Press, London. Unlike the heavy metal chalcogenides employed inintercalation compounds such as those reported in U.S. Pat. No.3,766,064, mixed oxides of the formula MOM'O₄ may be used without anyspecial pretreatment. Thus, the mixed oxide is heated with anappropriate Lewis base in a sealed tube at temperatures of from 100° to400° C., preferably 100° to 250° C. for up to about 21 days, preferablyfrom about 1 to 7 days. The amount of Lewis base is not critical and astoichiometric amount or an excess may be used. It is preferred toevacuate the tube prior to sealing to minimize the possibility ofoxidation of Lewis bases at elevated temperature. At higher temperaturessuch as 250° C., it is possible that the mixed oxide itself can lead tooxidation of Lewis base. It also is preferred to use substantiallyanhydrous Lewis bases. An alternative preparation is to reflux thehydrated mixed oxide with either the Lewis base or the Lewis basedissolved in suitable organic solvent.

The layered compounds of the present invention do possess the covalentbonding characteristic of molecular coordination compounds. They arenot, however, molecular coordination compounds since the layeredstructure of the mixed oxide is maintained even after reaction withLewis base.

As noted previously, the octahedra in mixed oxides of the formula MOM'O₄are very distorted with one very long and one very short metal oxygenbond. In the present invention, the very long metal oxygen bond isreplaced by a strongly bound Lewis base which then produces a truelayered compound by disrupting the weak interconnecting long metaloxygen bond. This is shown in FIG. 1, which is a schematic diagramillustrating the structure of (pyridine)VOPO₄. In order for the Lewisbase to fit on the surface of the MOM'O₄ layer, it should not besterically hindered, i.e., larger than the available space in the metaloxide structure. Thus, bulky Lewis bases such as tri-t-butyl amine andtriphenylphosphine will not form layered compounds according to theinvention.

When a bidentate Lewis base is incorporated into the mixed oxidestructure, separate layers of the mixed oxide are bridged or crosslinkedby covalent bonding resulting from the bifunctional Lewis base. This inturn yields a 3-dimensionally bonded structure composed of MOM'O₄ layersconnected by bidentate Lewis base molecules. Monofunctional Lewis basessuch as pyridine give rise to 2-dimensionally bonded layered structures.Both the 2- and 3-dimensionally bonded structures are true layeredcompounds even though the nature of the interlayer forces are quitedifferent for the respective cases. The bridged layered compounds haveformulae (1,4-diazabicyclo[2,2,2]octane)₀.5 MOM'O₄ and ##STR4## where Mand M' are defined above, n is 0 or 1 and R² is methylene; alkylene,alkenylene or alkynylene of 2-6 carbon atoms; C₆ -C₁₀ aryl; C₇ -C₁₄aralkylene; oxygen or sulfur. Especially preferred is ##STR5##

An X-ray powder pattern analysis of the layered reaction productsdemonstrates that the interlayer distance has increased in a mannercorrelating with the incorporation of specific Lewis bases between thelayers. For example, (pyridine)VOPO₄ and (pyridine)VOAsO₄ showinterlayer spacings of 9.59 and 9.66 Å; respectively, which agrees wellwith predicted values assuming that pyridine is coordinatedperpendicular to the MOM'O₄ layer. The corresponding VOSO₄ and NbOPO₄pyridine compounds show interlayer spacings of 9.0 and 9.2 Å,respectively. The fact that temperatures substantially in excess of theboiling point of the Lewis base are required to remove the Lewis baseprovides evidence of the covalent bonding present in the instant layeredcompounds. An example of a bridging Lewis base is 4,4'-bipyridine whichwhen incorporated into VOPO₄ results in the layered compound(4,4'-bipyridine)₀.5 VOPO₄. An interlayer spacing of 13.3 Å is obtainedfrom X-ray analysis. This is in close agreement with the predicted valueof 13.2 Å which can be determined from the known configuration of Vatoms in adjacent layers, known bond distances for 4,4'-bipyridine andV-N covalent bond distances for known V-pyridine compounds.Thermogravimetric analysis indicates the loss of Lewis basecorresponding to approximate compositions wherein x in L_(x) MOM'O₄ranges from about 0.5 to about 1.

The compounds of the invention possess unique properties and have a2-dimensionally or 3-dimensionally bonded layered structures. They aresemi-conductors or insulators, are transparent to electromagneticradiation, and are useful in electrochromic devices and as batterycathodes in lithium batteries as described in e.g., U.S. Pat. No.4,049,887.

The following examples are further illustrative of the invention.

EXAMPLE 1

VOPO₄.2H₂ O was refluxed in pyridine for 4 days. After this time theexcess pyridine was replaced with fresh pyridine and reflux continuedfor a further 6 days. The final yellow product was separated byfiltration and an X-ray powder pattern recorded. The lines in the X-raypattern could all be indexed on a tetragonal unit cell (a=6.21 andc=9.62 Å). No reflections due to starting VOPO₄.2H₂ O were observed.Thermogravimetric analysis of the compound in oxygen to VOPO₄ at 600° C.gave an overall weight loss of 32.2% compared to a theoretical weightloss of 32.8% for a stoichiometric 1:1 pyridine:VOPO₄ composition. Theinfrared spectrum of the compound showed strong absorptions at 1446,1489 and 1604 cm⁻¹ characteristic of coordinated pyridine. Electron spinresonance indicated 2.5 mole % of V(IV).

EXAMPLE 2

Anhydrous VOPO₄ was heated with excess pyridine in a sealed pyrexampoule for 4 days at 170° C. The yellow product was separated byfiltration and analyzed by X-ray diffraction and thermogravimetricanalysis. Thermogravimetric analysis in oxygen gave an overall weightloss of 29.4% compared with the theoretical of 32.8% for the 1:1stoichiometry. An X-ray powder pattern could be completely indexed onthe same tetragonal cell as in Example 1 but with slightly differentlattice parameters (a=6.20, c=9.52 Å). Electron spin resonance indicated1.5 mole % of V(IV) in the final product. The infrared spectrum issimilar to that obtained in Example 1 and shows strong absorptions at1444, 1487 and 1602 cm⁻¹.

EXAMPLE 3

VOPO₄.2H₂ O, excess pyridine and activated molecular sieves were heatedat 150° C. for 4 days in a sealed pyrex ampoule. The green product wasseparated from excess pyridine and the molecular sieves andcharacterized as described above. By thermogravimetric analysis theoverall weight change of 32.7% is close to that for a stoichiometric(pyridine)VOPO₄ complex. The compound prepared by this technique,however, differs in color and in the extent of vanadium reductionindicated by the electron spin resonance (18 mole %). Moreover, thethermogravimetric analysis indicates that the major pyridine loss occursat about 450° C. compared to about 300° C. for the compounds of Examples1 and 2. The infrared spectrum is also characteristically different inshowing a strong absorption at 1570 cm⁻¹.

EXAMPLE 4

Hydrated vanadyl sulfate was dried at 160° C. for 20 h to give VOSO₄.XH₂O. Anhydrous VOSO₄ was obtained by further dehydrating VOSO₄.H₂ O at260° C. in helium for 4 h and 350° C. for 1/2 h. The anhydrous VOSO₄ wassubsequently handled in a dry box to prevent rehydration. AnhydrousVOSO₄ and excess dry pyridine were heated in a sealed pyrex tube for 7dat 110° C. The X-ray powder pattern of the product gave a line at d=8.98Å characteristic of the formation of a pyridine compound. A small amountof unreacted VOSO₄ was also observed. Analysis by thermogravimetricoxidation to V₂ O₅ gave a pyridine:VOSO₄ ratio of 0.94:1.

EXAMPLE 5

Anhydrous VOPO₄ was heated with a solution of 4-phenylpyridine in xylenein a sealed pyrex tube for 4 days at 150° C. After this period, thesample was removed, reground and resealed. The reaction was continuedfor a further eight days at 200° C. X-ray diffraction of the productrevealed a series of 001 reflections corresponding to a layer separationof 14.3 Å. The layer separation is increased relative to that observedfor the pyridine compound in Example 1 due to the larger size of the4-phenylpyridine. Thermogravimetric oxidation to VOPO₄ indicated anoverall composition of 0.42 4-phenylpyridine per VOPO₄. Some unreactedVOPO₄, however was observed in the X-ray pattern.

EXAMPLE 6

VOAsO₄.2H₂ O was synthesized by a modification of the proceduredescribed N. G. Chernorukov et al. in the Russian Journal of InorganicChemistry, 23, 1479, 1978. V₂ O₅ (3 g) and H₃ AsO₄.1/2H₂ O were refluxedin 75 ml of water for 3 days. The resulting yellow brown solution wasfiltered while hot and then reduced to one quarter of its originalvolume. Yellow VOAsO₄.2H₂ O separated and was removed by filtration,washed and dried. Anhydrous VOAsO₄ was prepared from the hydratedcompound by heating at 200° C. in flowing helium for two hours. Theanhydrous VOAsO₄ was subsequently handled in a dry box to preventrehydration.

Anhydrous VOAsO₄ was heated with excess dry pyridine at 150° C. in asealed pyrex tube for 10 days. The X-ray powder pattern could be indexedon a tetragonal unit cell with a=6.41 Å and c=9.70 Å together with linesdue to a small amount of unreacted VOAsO₄. Thermogravimetric analysis ofthe compound in oxygen to VOAsO₄ gave a weight loss of 26.9% comparedwith the theoretical weight loss of 27.8% for the stoichiometric 1:1pyridine:VOAsO₄ composition. The infrared spectrum showed strongabsorptions at 1446, 1485 and 1602 cm⁻¹ characteristic of coordinatedpyridine.

EXAMPLE 7

In an inert atmosphere dry box, 0.395 g anhydrous 4,4'-bipyridine, 0.500g VOPO₄.2H₂ O, and 10 ml dry toluene were placed in a pyrex ampoulealong with activated 4 A molecular sieves. The tube was removed from thedry box, cooled in liquid Nitrogen, evacuated and sealed. The sealedtube was then heated at 110° C. in oven for 3 days, cooled, and openedin the dry box. Molecular sieves were removed and a yellow solid productwas separated from the clear supernatant by filtration, washed threetimes with 5 ml toluene, and sucked dry. An X-ray powder diffractionpattern showed slightly broadened lines (fwhm=0.4°-0.6°2θ) at d spacingsof 13.3, 6.57 and 4.43 Å, the first three lines in an 001 seriesindicating a layer spacing of about 13.3 Å. Thermal gravimetric analysesin oxygen to VOPO₄ indicated a stoichiometric (4,4'-bipyridine)₀.494VOPO₄.

What is claimed is:
 1. A composition of matter comprising the reactionproduct of a mixed oxide having layers of corner linked octahedra andtetrahedra and a nitrogen donor Lewis base, said reaction productforming a layered compound of the formula(1,4-diazabicyclo[2,2,2]octane)₀.5 MOM'O₄ or ##STR6## where MOM'O₄ is amixed oxide selected from the group consisting of VOPO₄, VOSO₄, VOAsO₄,VOMoO₄, NbOPO₄, NbOAsO₄, TaO PO₄ and MoOPO₄, n is 0 or 1 and R² ismethylene, C₂ -C₆ alkylene, alkenylene or alkynylene, C₆ -C₁₀ arylene,C₇ -C₁₄ aralkylene, alkylene, oxygen or sulfur, the layered compoundbeing characterized in that adjacent layers of MOM'O₄ are covalentlybound to said Lewis base.
 2. The composition of claim 1 wherein saidlayered compound is ##STR7##
 3. The composition of claims 1 or 2 whereinMOM'O₄ is VOPO₄, VOSO₄, VOAsO₄ or VOMoO₄.